This research program attempts to better define the structure and functional mechanisms of the central nervous system which participate in visual pattern discrimination and visual attention in cats and monkeys. Particular emphasis is placed upon the pulvinar and regions of the cortex to which it projects, including inferotemporal, striate, and extrastriate cortex. Five major areas of investigation are outlined: 1. Identification of the sources and nature of functional visual input to the pulvinar, 2. Determination of the interrelationships and interactions of the pulvinar with visual and association cortex, 3. Use of the pulvinar as a model system for conditioning and plasticity of its individual neurons, 4. Role of the pulvinar and inferotemporal cortex in visual attention and visual pattern discrimination learning and retention, and 5. Involvement of the pulvinar in attention and perceptual learning associated with eye movements, fixations and visual tracking behavior. Methods include electrophysiological recording (single unit and average evoked potentials), electrical stimulation, reversible cryogenic blockade, electrolytic lesions, and behavioral training techniques designed to separate attentional and visual discriminative processes. Current work is predominantly with Nemestrina and squirrel monkeys. In the Nemestrina monkey training in the discrimination ability testing apparatus (data) involves discrimination of two patterns appearing briefly (10 msec) on two adjacent stimulus panels and requiring a high degree of alertness and attention. The effect on such performance of cryogenic blockade of inferotemporal cortex and prestriate cortex will be tested for both old and new learning. In squirrel monkeys the major emphasis is now on identifying and localizing single cells in the pulvinar which have responses associated with spontaneous eye movements and trained voluntary eye movements. These studies of the second visual system have relevance for understanding some of the disorders attributed to the pulvinar and its cortical projection areas as in aphasia and dyslexia, as well as other higher cognitive functions. BIBLIOGRAPHIC REFERENCE: Perryman, K.M., Lindsley, D.B. Visual responses in geniculo-striate and pulvino-exrastriate systems to patterned and unpatterned stimuli in squirrel monkeys. Electroenceph. Clin. Neurophysiol., 1977, 157-177.